Resistor substitution for 20k? GGG Ibanez BP10 Compressor..

[gbkd80]

I'm putting together the BP10 project and in the BOM they never mentioned the 20k resistor that falls between C12 and VR4 which is the level pot. 

http://www.generalguitargadgets.com/pdf/ggg_ibp10_sc_mod.pdf

I did a huge parts order with Tayda, got 2 day DHL shipping and FORGOT to get 20k resistors... doh!  I have 22k and I put one in, figuring it can't be that far off, measuring like 21.5k (carbon film 5%).  Since the build is in progress i wanted to ask here if it should make a huge difference or not...

[stonerbox]

22k will probably do just fine. Do you have 10k resistors? Stick two together and you will get... 

[gbkd80]

22k will probably do just fine. Do you have 10k resistors? Stick two together and you will get...

Yeah, I know but I'm OCD about my builds so I'd have to "really" squeeze those together and make 'em look almost like one.  I guess if it sounds or works funny I'll know...

[Cozybuilder]

Its just 3 series resistances to control the signal level being fed to the output buffer. I'd use the 22K on hand- that just limits the max volume; the pot is a 0-100K variable resistance as your primary V control; the 1K is to give a minimal resistance above ground (in this application).

Edit:
You could think of it as a 123K  pot, with the wiper adjustable from 22K to 122K between signal and ground. Using a 20K resistor would give you a 121K pot, adjustable from 20K to 120K- you won't hear a difference between using a 20K or 22K. I doubt if the 100K pot will measure 100K, it has a wider allowable variance than the 1% on the carbon film resistor.

[PRR]

> should make a huge difference or not...

The diff is inaudible.

I don't even know why it has the 20K and 1K.

[gbkd80]

Well, which brings me to another interesting find...

I finished the build tonight, which of course doesn't work (my own etch).  The circuit isn't completing power, I can see that pretty clearly.  When I cross-examined the production PCB and the layout, the PCB itself looks like it has a set of built-in jumpers.  Take a look at the pic:

http://www.generalguitargadgets.com/wp-content/uploads/1m_ibpcp10_pcb.jpg

You'll see a jumper line running across R12, 15, 46 and landing at Q11.  There's also a jumper above it.  So, I duplicated this run on my etch board just now and clearly it still doesn't work, but wouldn't it appear that the self-etch layout is possibly incorrect if there's jumpers in the production board?  Has anyone actually built one of these from their own etch and have it work? 

[Cozybuilder]

The traces on the dual sided production board are most likely laid out different than the single sided self etch. comparing these two for troubleshooting just isn't going to be productive. Best to print out the schematic, and verify that each component is connected on your PCB as shown on the schematic. It takes time. Of course, verify your power connections are made correctly first. The GGG layout looks right.

[J0K3RX]

Well, which brings me to another interesting find...

I finished the build tonight, which of course doesn't work (my own etch).  The circuit isn't completing power, I can see that pretty clearly.  When I cross-examined the production PCB and the layout, the PCB itself looks like it has a set of built-in jumpers.  Take a look at the pic:

http://www.generalguitargadgets.com/wp-content/uploads/1m_ibpcp10_pcb.jpg

You'll see a jumper line running across R12, 15, 46 and landing at Q11.  There's also a jumper above it.  So, I duplicated this run on my etch board just now and clearly it still doesn't work, but wouldn't it appear that the self-etch layout is possibly incorrect if there's jumpers in the production board?  Has anyone actually built one of these from their own etch and have it work?

Actually, you're right..  After looking at the diy etch layout I spotted a whole bunch of unconnected components, pads not connected to anything and no pads for the jumpers that are obviously needed. Nowhere in the docs does it even mention anything in regards to all of these disconnects? After looking at that I would salvage all your parts from the board and look for the layout elsewhere or make your own!! Good grief man... that is a shame!

[gbkd80]

Well, which brings me to another interesting find...

I finished the build tonight, which of course doesn't work (my own etch).  The circuit isn't completing power, I can see that pretty clearly.  When I cross-examined the production PCB and the layout, the PCB itself looks like it has a set of built-in jumpers.  Take a look at the pic:

http://www.generalguitargadgets.com/wp-content/uploads/1m_ibpcp10_pcb.jpg

You'll see a jumper line running across R12, 15, 46 and landing at Q11.  There's also a jumper above it.  So, I duplicated this run on my etch board just now and clearly it still doesn't work, but wouldn't it appear that the self-etch layout is possibly incorrect if there's jumpers in the production board?  Has anyone actually built one of these from their own etch and have it work?

Actually, you're right..  After looking at the diy etch layout I spotted a whole bunch of unconnected components, pads not connected to anything and no pads for the jumpers that are obviously needed. Nowhere in the docs does it even mention anything in regards to all of these disconnects? After looking at that I would salvage all your parts from the board and look for the layout elsewhere or make your own!! Good grief man... that is a shame!

Wow, great... glad it's not just me then.  Thanks for noticing as well... I sent GGG an email the other night, we'll see what they say...

[LightSoundGeometry]

whenever I am off I use the next highest value, and pretend it has mojo nos drift 

[gbkd80]

I confirmed with JD Sleep that the etch layout is missing some jumpers.  From JD:

Yes, it looks like I forgot to put the jumper placement on the wiring diagram.  The bottom layer is correct and the same as the production PCBs.  There are 3 jumpers on the top layer so I think you may have missed that there is also a jumper from Q7 to Q8 (emitter to emitter).  I'll post the jumpers on the site page when I get a chance.  It seems that it's confusing to some folks who buy the PCB when I post jumper positions that are already built in to the top layer, but I'll try to clarify this.  Thanks for letting me know about this. 

Posted only for reference, in case anyone else tries this build and gets a surprise (or, letdown lol!)  Looks like I may have also missed the Q7 to Q8 jumper.

[gbkd80]

Well, it's working... can't say I'm instantly impressed with the sound, but I'm also using the wrong taper pot on the sustain (calls for a reverse log, I only have a regular 500k log pot).  Because of this I'm wondering if that's why the attack control doesn't seem to want to do much... anyway, reason it didn't work even with the jumpers in place is because I had a blown BA6110... got lucky and had 2 spares in the drawer that I forgot about and that got it going.